1. Field of Invention
This invention relates to a multi-purpose register, and more particularly, to one which can be used with data and control paths having different widths.
2. Description of the Prior Art
MOS field effect transistor gates have a relatively simple structure which require fewer masking steps in their fabrication than are required for bipolar transistor gates. This, in turn, allows for tighter design tolerances such that MOS circuits can be fabricated with high-packing densities in the creation of large memory arrays and microprocessors to be placed upon a single integrated circuit chip. However, bipolar transistor gates have higher switching speeds which are desirable in building larger main frame processors that can process much larger volumes of data than can microprocessors of the type referred to above.
In the past, many large main frame processors employing bipolar logic integrated circuits required many thousands of such integrated circuit chips and each chip or group of chips had to be separately designed to create the appropriate registers and other logic that went to form the processor. In each case, different sets of masks had to be created for each type of chip with a resulting delay in design time as well as fabrication time. Also, the costs involved often forced the designer to go to standard "off-the-shelf" type of integrated circuit chips so that the processor design had to be compromised as to its performance. This large number of bipolar integrated circuit chips resulted from the fact that the bipolar transistor structure is more complex than that of a MOS field effect transistor with a resultant increase in the number of masking steps required in its fabrication and a loosening of design tolerances so that packing densities cannot be achieved with bipolar logic that could be achieved with MOS logic.
In the past few years, various bipolar integrated circuit houses have begun supplying a set of logic chips which are referred to as "gate array" logic wherein different sets of chips are provided with a family of logic gates such as flip-flops, multiplexors, input gates and output gates. Before the chips are diced from their wafer, they are interconnected by a metallization process in accordance with the circuit design specified by the computer circuit designer to form a customized integrated circuit chip. In this manner, the integrated circuit house can achieve volume production of wafers at lower costs and the circuit designer specifies the integrated circuit chip having a particular set of logic gates on it and how they are to be interconnected to achieve the circuit and function desired. The circuit designer can now design the particular set of registers and other logic circuits that he wants without incurring the higher cost of not buying "off-the-shelf" circuits.
A particular component that is widely used throughout a processor is the register. Furthermore, such registers are used not only in the data paths of the processor but also in the information control paths for both instructions and other information such as literal values, etc. Thus, there is not one standard register that can be used throughout the processor. It is therefore advantageous to be able to obtain a bipolar register chip that can be used for all or many of the various purposes for which registers are employed without having to design separate registers for the semiconductor manufacturer, who, in turn, has to make separate sets of masks and go through the various processing steps of fabrication for each register. With the advent of gate array integrated circuits, it is now possible to design such a register.
It is then an object of the present invention to provide a multi-purpose register that can be used for various data and control paths which nevertheless have different path widths.
It is another object of the present invention to provide a multi-purpose register which can operate in different modes according to control signals provided so as to set the register's width to achieve different numbers of bits.
It is still a further object of the present invention to provide such an improved multi-purpose register that can be set to any number of bits wide from one bit up to the total number of flip-flops in the register.